The present invention relates to the fabrication of thin film inductive heads for data storage systems. More particularly, the invention relates to the formation of the top pole and improving the width control thereof.
Thin film inductive read/write heads are used for magnetically reading and writing information on a magnetic storage medium, such as a magnetic disc, which moves relative to the head. A thin film inductive head comprises a pair of "poles" which form the magnetic core of the head. Electrical conductors (or coils) pass between the poles and are used for reading information from and/or writing information to the magnetic storage medium. A gap region occupies a small space between two pole tips of the magnetic core. During a write operation, electrical current is caused to flow through the coils generating a magnetic field in the core. The write current in the coils causes magnetic flux to span the gap region. This magnetic flux is then used to impress the magnetic field upon a storage medium, which is then recorded. Reversal of the write current induces variations in the magnetic recording which convey information. During a read operation, the transitions on the storage medium induce reversals of magnetic flux in the core which induces changes in electrical signals in the coils. The changing electrical signals in the coils may be sensed with electric circuitry which enables the recovery of information stored on the magnetic medium.
Four main elements of a thin film inductive head are a bottom magnetic pole, a gap material which provides spacing between the poles, one or more levels of electrical conducting coils interposed within insulation layers, and a top magnetic pole.
During a typical formation process, the bottom magnetic pole is formed on a substrate. Typically, the bottom magnetic pole has a wider region called the "paddle" and a narrower region called the "tip." After the bottom magnetic pole is formed, a gap material is deposited on the entire surface of the bottom magnetic pole. Electrical conducting coils are then interposed between insulation layers over the bottom magnetic pole in the paddle region. These layers of insulation and coils in the paddle region create a hill sloping from the paddle region to the pole tip. Finally, a top magnetic pole is formed on the top insulation layer, following the contour of the hill.
Thin film inductive heads require the use of the top magnetic pole in order to complete the magnetic linkage path through the coil structure. It is important to correctly shape the top magnetic pole with predictably consistent dimensions for proper performance. The top pole can be pattern plated by using a photoresist layer which precisely determines the feature dimensions. Alternatively, the top pole can be patterned to final dimensions by ion milling with a sacrificial photoresist pattern.
For both of these methods of forming a top pole, a minimal thickness of photoresist must be used to achieve acceptable results. For pattern plating, the photoresist layer must be thicker than the plated top pole thickness to prevent overplating. Overplating is undesirable since an overplated region does not have well controlled vertical walls. Thus, the exact width dimensions of the top pole will vary from head to head depending on the severity of the overplating. In this way, it is difficult to manufacture inductive heads with predictable top pole widths. In addition, overplating can cause magnetic instability which will add to the overall instability of the inductive head. Poor overall performance is often the result.
Similarly, during the ion milling process, the sacrificial photoresist used must be thick enough to prevent any portion of the magnetic pole from being milled. When the sacrificial photoresist is too thin, some regions of the top pole can accidentally get milled. This causes severe damage to the inductive head and frustrates the performance.
The photoresist used in pole plating and in the ion milling process is often applied by a spin application. The combination of this application with the geometry of the hill causes the photoresist to be thinnest at the top of the hill. Typically, the fabricator will compensate for the thin coating by applying a thicker coating at the hill. This invariably causes even more thickness over the pole tip. The disadvantage of this correction is the increased difficulty in controlling the photoresist pattern within the pole tip region because of the increased thickness there. It becomes extremely difficult to form the required relatively narrow pole tip width when the photoresist on top of it is so relatively thick. A formation process and corresponding structure which could overcome these difficulties would be a significant improvement to the art.